An electric circuit is a path in which electrons from a voltage or current source flow.

The point where those electrons enter an electrical circuit is called the "source" of electrons. The point where the electrons leave an electrical circuit is called the "return" or "earth ground". The exit point is called the "return" because electrons always end up at the source when they complete the path of an electrical circuit.

Electronic circuits -usually use direct current sources. The load of an electronic circuit may be as simple as a few resistors, capacitors, and a lamp, all connected together to create the flash in a camera. Or an electronic circuit can be complicated, connecting thousands of resistors, capacitors, and transistors. It may be an integrated circuit such as the microprocessor in a computer.

Resistors and other circuit elements can be connected in series or in parallel. Resistance in series circuits is the sum of the resistance.